Neuropsychological functioning in first-episode schizophrenia

Background: Identifying neurocognitive subtypes in schizophrenia may help establish neurobiologically meaningful subtypes of the disorder, but is frequently confounded by differences in intellectual function between individuals with schizophrenia and controls. Aims: To examine neuropsychological performance in individuals with epidemiologically based, first-onset schizophrenia and intellectually matched controls. Method: Using standard IQ and reading tests, we examined the proportions of 101 people with epidemiologically derived, first-onset schizophrenia/schizoaffective disorder and 317 community controls, falling into three a priori defined intellectual categories: 'stable good', 'deteriorated poor' and 'stable poor'. Neuropsychological function was compared between intellectually matched participants with schizophrenia and control subgroups. Results: Multiple deficits in executive function, processing speed and verbal memory, but not visual/spatial perception/memory, were detected in all participant groups with schizophrenia compared with controls. The average effect size across the affected domains ranged from small to medium to large in the stable good, deteriorated poor and stable poor subgroups of participants with schizophrenia, respectively. Conclusions: Compared with intellectually matched controls, people with epidemiologically derived, first-onset schizophrenia/schizoaffective disorder show multiple deficits in executive function, processing speed and verbal memory.